An autofocus camera module disclosed in JP 9(1997)-18771 A is one example of a conventional camera module. FIG. 21 is a sectional view showing a configuration of this conventional camera module.
In FIG. 21, a voice coil motor 953 includes a drive coil 920, a bobbin 922, a center yoke 923, and a permanent magnet 924. A movable base 952 is connected to the bobbin 922. The center yoke 923 is provided in a yoke fixing portion 990a of a fixed base 990. A lens 981 is provided in an opening 990e of the fixed base 990, and a lens 982 is provided in an opening of the center yoke 923.
In this camera module 900, a shaft-mounting plate 991 is fixed so as to be parallel to the yoke fixing portion 990a. To this shaft-mounting plate 991, one end of each of two guide shafts 951a and 951b extending in the optical axis direction of the lens 981 is connected. The other end of each of the two guide shafts 951a And 951b is connected to the yoke fixing portion 990a. Fitting holes 952a and 952b are formed in the movable base 952. The guide shafts 951a and 951b are fitted in the fitting holes 952a and 952b, respectively. Thus, the movable base 952 is supported so as to be movable in the optical axis direction of the lens 981. An opening 952c is formed in a front portion (a portion on a side closer to the lens 981) of the movable base 952, and a CCD (Charge Coupled Device) 902 is fixed firmly to a rear portion (a portion on a side farther from the lenses 981 and 982) of the movable base 952. Optical filters 983, 984, and 985, such as an infrared cutoff filter, an optical LPF, and the like, are arranged on the front side (the side closer to the lens 981) of the CCD 902.
Next, the operation of the conventional camera module 900 shown in FIG. 21 will be described. Incident light enters the camera module 900 via the lenses 981 and 982, passes through the opening 952c to reach the CCD 902 via the optical filters 983, 984, and 985, whereby an image is formed on CCD 902. The CCD 902 photoelectrically converts the incident light into an electric signal, which then is output from the CCD 902.
The drive coil 920, the bobbin 922, the movable base 952, and the CCD 902 constitute a movable portion 960. When a current flows through the drive coil 920, the movable portion 960 is guided by the guide shafts 951a and 951b and integrally moves in the optical axis direction. An autofocus operation is performed by changing the relative distance between the lenses 981 and 982 and the CCD 902 in this manner. That is to say, an autofocus function is performed by controlling the current flowing through the drive coil 920.